1. Field of the Invention
This invention lies in the field of seismic recording and processing apparatus and methods. More particularly, it lies in the field of vibratory seismic methods. Still more particularly it lies in the field of vibratory seismic methods using a plurality of different sweeps on successive repetitions of the source, whereby the generation of side lobe correlation noise is minimized.
2. Description of the Prior Art
It is well known in the seismic art that since the inception of the vibratory source-correlation systems, some 20 years or more ago, such operations have always been carried out with a plurality of repetitions of the vibratory source at the same point on the earth, and with the same sweep signal. The plurality of received signals were then straight stacked and then correlated with the sweep.
It is, and was, well known also, that in correlating a vibratory signal (such as a reference sweep) with a facsimile of itself, that there were always side lobes recorded as by-products of the correlation. It was known that these side lobes were due to the limited band width of the sweep, and that the wider the frequency bandwidth, the smaller the side lobes. It was also known that the longer the time duration of the sweep, the smaller the side lobes. However, because of the practical difficulties in doing much to improve these conditions, nothing was done.
It is therefore an important object of this invention to operate a vibratory seismic system in a manner to minimize the side lobe correlation noise.
It is a further object of this invention to provide minimum correlation noise while also improving the processing of the signals.